This paper presents the design and analysis of a multimedia system-on-chip consisting of the H.264 encoder implemented on a multiprocessor architecture. A model-driven approach is adopted by using the standard MARTE profile of UML. An abstract clock analysis is applied to deal with the correctness of the system temporal properties and to find the most suitable execution platform configurations regarding the energy consumption. We claim that our approach allows for an early design space exploration, which is crucial when implementing modern complex systems.